handle nil drop list in otel sampler

[dnsbty]

I'm not completely sure if there's another root issue at play here, but I updated my codebase to use 11.0.0 and set up the configuration to start sending traces to Sentry, and got the following error reported to Sentry:

Protocol.UndefinedError: protocol Enumerable not implemented for nil of type Atom. This protocol is implemented for the following type(s): DBConnection.PrepareStream, DBConnection.Stream, Date.Range, Ecto.Adapters.SQL.Stream, File.Stream, Function, GenEvent.Stream, HashDict, HashSet, IO.Stream, Jason.OrderedObject, List, Map, MapSet, Phoenix.LiveView.LiveStream, Postgrex.Stream, Range, Req.Response.Async, Stream
  File "lib/enum.ex", line 1, in Enumerable.impl_for!/1
  File "lib/enum.ex", line 194, in Enumerable.member?/2
  File "lib/enum.ex", line 2009, in Enum.member?/2
  File "lib/sentry/opentelemetry/sampler.ex", line 38, in Sentry.OpenTelemetry.Sampler.should_sample/7
  File "/app/deps/opentelemetry/src/otel_sampler.erl", line 129, in :otel_sampler.should_sample/7
  File "/app/deps/opentelemetry/src/otel_span_utils.erl", line 118, in :otel_span_utils.sample/7
  File "/app/deps/opentelemetry/src/otel_span_utils.erl", line 59, in :otel_span_utils.new_span/9
  File "/app/deps/opentelemetry/src/otel_span_ets.erl", line 61, in :otel_span_ets.start_span/7

I believe this will fix the problem. I'm having a hard time finding any documentation of what the configuration given to the sampler should look like (the official type for it is just term()) so I don't think we can rely on it being an enumerable with the :drop key. Please let me know if I'm wrong on that though!

[solnic]

Thanks for catching this! I made a mistake in the CHANGELOG with the example config, it was supposed to be:

config :opentelemetry, sampler: {Sentry.OpenTelemetry.Sampler, [drop: []]}

It does make sense to make it optional of course, so this PR is good 🙇🏻

[solnic]

Would you mind updating the CHANGELOG too? 🙏🏻

[whatyouhide]

@solnic we generally autoupdate the CHANGELOG on release and curate it on the maintainers side to avoid having to ask contributors to do that 🙃

[solnic]

Gotcha. In other SDKs updating CHANGELOG is required for a PR to be merged though and we added Danger checks for this here too, although it doesn't seem to be working as it didn't leave a comment with suggested entry and I could still merge the PR 🙃